Showing papers by "Ulrich Platt published in 1994"

Spectroscopic measurement of bromine oxide and ozone in the high Arctic during Polar Sunrise Experiment 1992

Abstract: Bromine oxide (BrO) is proposed to be an important agent for tropospheric ozone depletion, as observed in the high Arctic during springtime. In this paper we report measurements of bromine oxide and ozone by Long Path Differential Optical Absorption Spectroscopy (LPDOAS), 8.6-km light path), performed in April 1992 in Alert (82.3°N, 62.2°W). BrO mixing ratios were found between the detection limit of about 4 ppt to 17 ppt. Because of the frequently poor visibility conditions, especially during ozone depletion events, long-signal integration times (sometimes more than 24 hours) were needed, and short-time BrO-peaks might have escaped detection. A pure in situ chemical mechanism based on BrO-catalyzed ozone destruction cannot account for the observed complete depletion of ozone at the observed BrO mixing ratios. On the other hand, it can be argued that the maximum time for chemical ozone depletion (by any mechanism) may not be much longer than 1 day. A simple scenario involving a combination of advection, atmospheric dispersion, and BrO-catalyzed chemical ozone destruction is described, which could explain the observed ozone loss.

Nitrate Radicals in Tropospheric Chemistry

Abstract: Nitrate radicals are being recognized as key intermediates in a growing list of important chemical processes in the atmosphere. Here, the role of nitrate radicals (NO3) in tropospheric chemistry is discussed, with special emphasis on results from field measurements, most of which have been made by differential optical absorption spectroscopy (DOAS), with matrix-isolation electron spin resonance being an alternative technique. Nitrate radicals were observed in the atmosphere at peak mixing ratios of 350 ppt. Long-term observation of NO3 shows that 24-h averages in rural air masses are closer to a few ppt. Nevertheless, the NO3 radical plays an important role in the non-photochemical conversion of NOx to HNO3. Also, NO3 is a strong oxidizing agent and initiates the night-time removal of atmospheric trace species such as olefins, aromatic hydrocarbons, and organic sulfur compounds. Finally, night-time peroxy radical production and release of reactive halogen species from sea salt aerosol might be initiated by NO3 reactions.

Airborne measurements during the Arctic Stratospheric Experiment: Observation of O3 and NO2

Abstract: During winter 1991/92 DOAS (Differential Optical Absorption Spectroscopy) measurements were performed from a C130 Transall aircraft within the framework of the EASOE (European Arctic Stratospheric Ozone Experiment) campaign. The campaign extended from Dec. 1991 until March 1992 with a series of flights in the Arctic (60°W to 60°E, 85°N to 48°N). Two spectrometers were operated on the aircraft: an UV-instrument (see Brandtjen et al., this issue) and a DOAS-vis instrument to detect O3, O4, NO2 and NO3 in the visible band (363 nm–680 nm). The DOAS-vis ozone measurements were largely influenced by the presence of the Mt Pinatubo aerosol cloud. A correction of the data by actual Mie-profiles is described. A NO2 depletion with minimum values of 2.3*1014/cm² in Jan. 92 was observed. Occasionally, OClO could also be detected.

An overview of the EASOE Campaign

Abstract: The scientific planning of the EASOE campaign is outlined and the various constituent and meteorological data sets are described.